This interceptor binds a new JPA EntityManager to the thread before a method
call, closing and removing it afterwards in case of any method outcome.
If there already is a pre-bound EntityManager (e.g. from JpaTransactionManager,
or from a surrounding JPA-intercepted method), the interceptor simply participates in it.

Application code must retrieve a JPA EntityManager via the
EntityManagerFactoryUtils.getEntityManager method or - preferably -
via a shared EntityManager reference, to be able to detect a
thread-bound EntityManager. Typically, the code will look like as follows:

public void doSomeDataAccessAction() {
this.entityManager...
}

Note that this interceptor automatically translates PersistenceExceptions,
via delegating to the EntityManagerFactoryUtils.convertJpaAccessException
method that converts them to exceptions that are compatible with the
org.springframework.dao exception hierarchy (like JpaTemplate does).

This class can be considered a declarative alternative to JpaTemplate's
callback approach. The advantages are:

no anonymous classes necessary for callback implementations;

the possibility to throw any application exceptions from within data access code.

The drawback is the dependency on interceptor configuration. However, note
that this interceptor is usually not necessary in scenarios where the
data access code always executes within transactions. A transaction will always
have a thread-bound EntityManager in the first place, so adding this interceptor
to the configuration just adds value when fine-tuning EntityManager settings
like the flush mode - or when relying on exception translation.

setExceptionConversionEnabled(boolean exceptionConversionEnabled)Deprecated. Set whether to convert any PersistenceException raised to a Spring DataAccessException,
compatible with the org.springframework.dao exception hierarchy.